Patent GB-819986-A (GB)
Title: Arrangements for the supervision of line conditions in telecommunication systems, especially in telephone systems
IPC: H04M15/04
Filed: 1957-10-04
Abstract: 819,986. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Oct. 4, 1957 [Oct. 5, 1956], No. 31162/57. Classes 40 (4) and 40 (9). A device for determining the open circuit or closed circuit condition of a line comprises a saturable device which is saturated in one condition of the line but supersaturated in the other. In one embodiment, Fig. 2 (not shown), a saturable core carries four windings, one of which biases the core to saturation and another coil carries line current so that when the line loop is closed the core is supersaturated. A further winding applies pulses whose field opposes that of the other two so that when the core is saturated (not not supersaturated) it can drive the core around its hystersis loop, thereby inducing a pulse in a detector winding. Alternatively the biasing winding may be supersaturate the core and the field due to the current from the line winding may be in opposition so as to bring the core to the point where it is just saturated. The cores for the various lines may be arranged in a co-ordinate array, Fig. 5 (not shown), the pulse applying coil being replaced by two coils, the first of which are connected in series in horizontal rows and the second of which are connected in series in vertical columns, it being arranged that both coils of a core must be pulsed before an output is obtained. Thus in one 4 X 5 embodiment the five columns and four rows are cyclically pulsed, each column pulse straddling a whole cycle of row pulses. Alternatively, each long pulse may be replaced by a series of shorter pulses, each shorter pulse straddling a pulse of the other series. In order to prevent the impulses causing disturbances in the subscriber's line, the core K, Fig. 8, carrying the line current and biasing windings I and IV may have a hole through which the pulse application coils IIx, IIy and the induced pulse detection coil III are passed. The biasing winding IV may also be passed through the hole, Fig. 9 (not shown). If the line is provided with a line transformer, the transformer core M, Fig. 10, may be provided with a gap to accommodate the pulse core K. The outer ends of windings UeI1, UeII1 are connected to line and the inner ends connected to a feed battery and a shunt condenser. Windings UeI2, UeII2 are connected in series via a condenser and are connected to the exchange. Coils II, III and IV are the pulse supply, induced pulse detection and biasing windings respectively. The core K must saturate much more quickly than the core M. Arrangements may be provided for neutralizing the small pulses in the read-out windings of cores associated with closed loops, due to the saturation characteristics being not truly horizontal. Thus, as shown in Fig. 12, in which each core is tested in turn by means of a long pulse on one of leads X1 ... X4 and a short pulse on one of leads Y1 ... Y3, each short pulse also passes through primary windings IIycl ... IIyc4 of transformers whose secondaries are connected in series opposition to the common read-out circuits from all the read-out coils III and produce a small voltage sufficient to cancel out the unwanted signals.